Low back pain is common, and in most cases, it improves without surgery. But severe back pain can be a symptom of a serious condition that is not well known and is often misdiagnosed. Cauda equina syndrome (CES) occurs when the bundle of nerve roots at the lower end of the spinal cord (cauda equina) are compressed and disrupt motor and sensory function to the lower extremities and bladder. Patients with this syndrome are often admitted to the hospital as a medical emergency. CES can lead to incontinence and even permanent paralysis.
The collection of nerves at the end of the spinal cord is known as the cauda equina, due to its resemblance to a horse’s tail. The spinal cord ends at the upper portion of the lumbar (lower back) spine. The individual nerve roots at the end of the spinal cord provide motor and sensory function to the legs and the bladder. The cauda equina is the continuation of these nerve roots. These nerves send and receive messages to and from the lower limbs and pelvic organs.
Symptoms
The symptoms of cauda equina syndrome can vary, but the key signs doctors look for are:
- Severe low back pain and sciatica
- Pain may be sudden and severe or gradually develop over weeks
- Motor weakness, sensory loss, or pain in one, or more commonly both legs
- Difficulty passing urine or using the bowels
- Prolonged inability to pass urine can result in urine leaking uncontrollably
- Numbness or tingling in the groin (“saddle region”)
- Sexual dysfunction
Causes
Cauda equina most commonly occurs when a disc in the back pushes out of place and compresses the spinal cord (see Disc Herniation). Usually this needs to be a severe herniation to cause cauda equina.
Other causes of cauda equina include:
- Spinal canal stenosis with a smaller disc prolapse
- Trauma to the spine
- Rare causes include infection in and around the vertebral bones (see osteomyelitis), cancer in the spine, after injections into the spine or spine surgery.
Risk Factors
Risk factors for developing cauda equina syndrome include:
- A history of low back pain with sciatica, especially sciatica in both legs.
- Instability or deformity of the spine
- Trauma to the spine, often following a car accident
- Recent lumbar spine surgery
- A history of cancer
- Recent severe infection
- Cauda equina syndrome can develop suddenly even without these risk factors.
Investigations
Cauda equina syndrome is an emergency, and these tests are arranged urgently rather than at a routine appointment. If your doctor suspects it, you will usually be sent straight to hospital rather than asked to wait for an outpatient scan.
Examination
Your doctor will check the things the cauda equina nerves control:
- the power, sensation and reflexes in both legs
- sensation around the back passage, buttocks and inner thighs — the “saddle” area
- the tone and squeeze of the muscle around the back passage
- how well your bladder is emptying
Bladder scan
A small ultrasound scan measures how much urine is left in your bladder after you pass water. A large amount left behind is one of the more reliable early signs, and it can be present before you notice anything wrong yourself.
MRI scan
An urgent MRI of the lower spine is the test that confirms the diagnosis. It shows the discs, the nerve roots and anything pressing on them, and tells the surgeon exactly where the compression is and what is causing it.
If you cannot have an MRI
A CT scan with dye injected around the nerves — a CT myelogram — can be used instead if an MRI is not possible, for example if you have a pacemaker or certain metal implants.
None of these tests should delay getting to hospital. Where the picture is convincing, assessment and scanning happen alongside referral, not before it.
Complications
Complications are increasingly likely if diagnosis and appropriate management is delayed, and include residual:
- Paralysis
- Sensory abnormalities
- Bladder, bowel, and sexual dysfunction
Treatment
Cauda equina syndrome is treated with surgery to take the pressure off the nerves. There is no course of medication, injection or physiotherapy that treats it, and delay makes a full recovery less likely.
Surgery to decompress the nerves
The operation removes whatever is pressing on the cauda equina. Most often that is disc material that has pushed backwards into the spinal canal, so the surgeon removes the fragment — a discectomy — and, if more room is needed, part of the bony arch at the back of the vertebra, called a laminectomy. The aim is to relieve the pressure before the nerves are permanently damaged.
How quickly
Sooner is better. Surgery is arranged as an emergency, and the aim is to decompress the nerves within 24 hours of the diagnosis being made. In practice that often means operating overnight or on the next available list rather than at a planned date. Exactly how much difference each additional hour makes is still debated among surgeons and you may see different figures quoted, but the outlook is better the earlier the pressure is relieved.
If the cause is not a disc
Where a tumour, infection or fracture is compressing the nerves, the surgery is different and other treatment usually runs alongside it — antibiotics for an infection, or steroids and cancer specialist input for a tumour. Your team will explain what applies in your case.
Your bladder in the meantime
A catheter is usually placed to drain the bladder before surgery and stays in for a period afterwards. This protects the bladder from being over-stretched while the nerves recover.
After the operation
Leg pain often settles quickly once the pressure is off. Power, sensation, bladder, bowel and sexual function recover more slowly, and improvement can continue over many months. Some people recover completely. Others are left with lasting problems, most often with bladder, bowel or sexual function, and that risk is higher the longer the compression went unrelieved.
Recovery is supported by physiotherapy, and by continence nurses where bladder or bowel function is affected. Some people are taught to pass a catheter themselves while function returns.
Seeking Advice
Your Family Doctor (GP)
Your Family Doctor will be able to diagnose and help treat your problem. He or she will be able to
- tell you about your problem
- advise you of the best treatment methods
- prescribe you medications
- and if necessary, refer you to Specialists (Consultants) for further treatment
Prevention
Prevention of cauda equina syndrome is focused on early diagnosis by identifying the symptoms described. While low back pain with leg pain and/or weakness is a common complaint that affects many people, cauda equina syndrome is a rare complication. Your doctors should be vigilant in identifying these cases. You should familiarise yourself with the signs and symptoms that could suggest possible cauda equina syndrome, including change in bowel or bladder function and loss of sensation in the groin.
F.A.Q. | Frequently Asked Questions
How quickly do I need to be seen?
Immediately. Go to your nearest emergency department rather than waiting for a GP appointment. Cauda equina syndrome is one of the few genuine emergencies in spinal surgery, and the outcome depends heavily on how quickly the pressure is taken off the nerves.
I have back pain and sciatica — should I be worried?
Back pain and sciatica are common and are usually not cauda equina syndrome. What changes the picture is numbness in the saddle area — between the legs, around the back passage and genitals — difficulty passing or controlling urine, loss of bowel control, or weakness in both legs. Those symptoms are the ones that need emergency assessment.
What does “saddle numbness” actually feel like?
People describe it differently: not feeling the toilet paper, not knowing when the bladder is full, a numb or strange sensation when wiping or sitting, or reduced sensation during sex. It is often subtle rather than dramatic, which is part of why it gets missed.
Will I definitely need surgery?
If the diagnosis is confirmed, yes. There is no medication, injection or physiotherapy that treats cauda equina syndrome — the pressure has to be removed surgically.
Will I get full function back?
It varies, and it depends substantially on how much nerve damage had occurred before the pressure was relieved. Leg pain often settles quickly. Bladder, bowel and sexual function recover more slowly and improvement can continue for a year or more. Some people are left with permanent changes, which is why the urgency matters.
What if I went to hospital and was sent home?
If your symptoms change or get worse — particularly the bladder, bowel or saddle numbness — go back. Cauda equina syndrome can develop over hours or days, and an assessment that was reassuring yesterday does not rule it out today.